If you're not looking to have male clients, I'd say the easiest answer is 'give up now'.
But if you're determined... there are places you can advertise for free, but a) there is a LOT of competition (there are currently about four and half thousand very optimistic men looking to escort women on Adultwork alone) and b) not much demand - less than 1/2 percent of male escorts using one of the main specialist sexual health services had only female clients and only about one percent had any female clients.
The large majority of male escorts work independently, advertising on places like Gaydar. Some escort agencies exist - check the gay press for their ads.